Cellular radiotelephone service has been in use for some time and has traditionally been characterized by a central site transmitting with high power to a limited number of mobile units in a large geographic area of radiotelephone service, hereinafter referred to as a cell. Mobile transmissions, due to their lower power, are received by a network of receivers located remotely from the central site and then returned to the central site for processing. Digital cellular radiotelephone service may be similarly characterized. One major difference, however, is the use of digital voice and data channels which permit the efficient allocation of system resources via any of the well known multiple access schemes, such as, for example, Time Division Multiple Access (TDMA).
In a digital cellular radiotelephone communication system, each cell dedicates one or more communication channels as a Common Control Channel (CCCH). The CCCH is made up of several logical channels which provide different services to the mobile subscriber. The Random Access Channel (RACH) is used for receiving access requests from mobile subscriber units. The Access Grant Channel (AGCH) is used to instruct mobile subscriber units, via channel designation messages, to tune to a particular frequency and time slot where signalling may take place. The ECHO channel will identify the mobile that accessed on the previous uplink slot, will indicate that the previous slot was idle, or will indicate the occurrence of a collision. The Broadcast Control Channel (BCCH) is used to transmit cell specific parameters to the mobile subscribers tuned to the cell.
In digital cellular radiotelephone systems, there are several access procedures a requesting mobile unit can initiate when attempting to obtain and utilize system resources. These access procedures inform the system which type of operation a requesting mobile unit is attempting to perform. Such operations include but are not limited to, call origination, location reporting, registration and page response.
The typical access procedure may be summarized as follows. A mobile unit sends its system access request over the RACH, starts an access timer, and awaits a channel designation message from the Base Station System (BSS), which informs the mobile whether the access was successful. If the BSS fails to respond to the mobile unit before the access timer expires, the mobile will reissue its request. This procedure will continue until the mobile unit receives a valid confirmation, or until a maximum number of retries have been attempted, as defined by the BSS.
For identification purposes, each mobile unit's access request contains mobile identification information. Therefore, each BSS receives mobile specific information with which to distinguish one mobile unit's access request from that of another. Access requests, however, do not contain information pertaining to the number of previous requests. Whenever a mobile unit retransmits its access request there is no means for the BSS to determine whether the received request is the mobile's first or a subsequent attempt. It would be extremely advantageous therefore to provide a method for informing the BSS of the number of requests attempted by each mobile unit accessing the system, thereby providing the BSS with information vital for monitoring system performance and reducing levels of contention between two or more mobiles requesting the same resources at the same time.